Devhook 5.2 PSP fw 1.5 (newbie questions)

Just got myself a PSP with fw 1.5. I want to install Devhook 5.2 to run the latest images. Can some one tell me if Devhook has to be flashed to rom or can it be installed on the memory stick. I dont want to start flashing in case I brick it.

I wouldnt say there's much risk. Im not lying when I say Ive done various downgrades / upgrades on about 25 PSPs and had no probs with any of em.
At some point you'll have to do it to keep up as Devhook wont progress any further now....just go for it !